<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        //undefined
        //var x;
        //alert(x)
        //字符
        var str1="柠檬"
        var str2='柠檬'
        console. log(str1)
        console. log(str2) 
       //var str1="柠檬';
       var str3="柠檬说:'熊出没'";
       console .log(str3)
       var str="JS"
       //JS中先运算等号右边的语句
       str=str+"柠檬";//字符串中+号是连续的意思JS柠檬
       console.log(str);
    </script>    
    </body>
</html>